The control of acid-base regulation by the kidney is critical in maintaining body electrolyte homeostasis and acid secretion is a cornerstone of this function. The specific purposes of this proposal are to examine the cellular mechanisms and modulators of acid secretion in cultured cells derived from the inner medullary collecting duct of the rat kidney. This cell culture line provides an excellent model for the study of distal epithelial cell acid-base function since these cells contain many, if not all, of the acid-base transporters that regulate distal protein secretion. Thus, this culture cell system provides a unique opportunity for determining the cellular signals that modify these transporters. To this end, techniques including fluorescent probes for monitoring cell pH and calcium, immunohistochemistry, protein electrophoresis, immunoblot, Northern blood and cofocal microscopy will be utilized. The intracellular events which are activated during acid secretion will be studied. These include the interrelationship among cell calcium, cell pH and acid secretion; the protein systems involved in acid secretion, i.e., H+-ATPase, carbonic anhydrase and the anion exchanger; the vesicle system necessary for acid secretion and its control including the cytoskeleton; the mechanisms of acidification adaption; and transepithelial transport. These studies will provide significant new information regarding the cellular mechanisms of acid secretion. Elucidation of the cellular mechanisms which occur in response to perturbations in acid-base status will provide invaluable information in helping to understand cellular transport mechanisms and the pathophysiology and management of acid-base disorders.